Offset product quality testing requirements and data usage (below)

7. Offset Printing and Printing Requirements for Ink and Density

1 The printing frame is evenly colored. The word "used" is used as the standard, and the fine product density is 0.27-0.33. The general product density is 0.25-0.35. In the classical Chinese, the word “person” or the same stroke is used as the standard, and the density data is the same as the “s”.

2 field density. The printing ink color density measurement value of the printing sheet is 0.9-1.3.

Fifth, the other requirements of the quality of flat print

1, overprint

Multi-color version of the image outline and location should be accurately nested, fine product overprint allowable error ≤ 0.10mm; normal print overprint allowable error ≤ 0.20mm. Offset printing and overprinting requirements; printing book page layout is positive and negative overprinting accuracy, its overprint tolerance error fine product is less than 2mm, the general product is less than 3mm.

2, appearance

1 layout clean, no trace of dirt.

2 The color tone of printing plate should be basically the same, the allowable error of fine product size is <0.5mm, and the allowable error of general product size is <1.0mm.

3 The text is complete, clear, and accurate.

3, outlets

1 dot gain control range

The network is clear and the angles are accurate and there is no ghosting. The enlargement value range of fine print outlets is 10%-20%; the increase value of general print outlets ranges from 10%-25%.

2 network point increase value calculation method

The dot gain value refers to the difference between the dot area of ​​a part of the printed matter and the dot area of ​​the corresponding color separation sheet. The formula is as follows

Printed dot area

A(%)=100%×[1-10-(DT-DO)]/[1-10-(DS-DO)]

Where: Do is the reflection density value of the non-printed part of the print,

Ds is the reflection density value of the printed matter in the field.

DT is the reflection density value at the site of the printed matter.

Color dot area

A(%)=100%×[1-10-(DT-DO)]/[1-10-(DS-DO)]

In the formula: Do is the transmission density value of the blank halftoning film,

Ds is the transmission density value on the film in the field.

DT is the transmission density at the site of the film. (table 3)

Color Do More Fine Print K Value General Print K Value
Y 0.25-0.35 0.20=0.30

M, C, BK 0.35-0.45 0.30-0.40

4, relative contrast (K value)

1K value control range

2 Calculation method of relative contrast

K=DS-DT/DS

Where: DS - measured solid density value

DT - Measured Dot Integral Density Value

The dot density values ​​of outlets are usually selected as 75% or 80% outlets. Because this is the area where the circular outlets begin to connect (the connection point is 78.54%), it is also the transitional area between the midtones and the undertones. The changes in the outlets in this area are the most significant for visual stimuli. It can reflect whether the printed matter has enough contrast levels and whether the ink layer is of moderate thickness or not.

5, overprint rate

The overprint ratio is a comparison of the ability of the ink to adhere to another ink. The factors that affect the ink overprint rate include ink layer thickness, ink stickiness, printing color sequence, and the interval between two color overprints. Poor overprinting can cause product color deviations and levels of disorder.

fD=D1+2-D1/D2×100%

Where: fD-overprint rate D1- first color density

D2 - Second Color Density D1 + 2 - First and Second Colors Overprint Density

If it is three-color overprint, find the overprint rate of the third color overprinted on the first two colors, and the relationship is:

fD=D1+2+3-D1+2/D3×100%

The superposition ratio of monochrome machine is usually 70%-80%, and the trap rate of four-color machine is about 60%.

Author: Jiangsu Press and Publication School